Proceedings with Extended Abstracts (single PDF file) - Radio ...

TOWARDS THE ADVANCED MEASUREMENTSOF ATMOSPHERIC TURBULENCE BY SPACED ANTENNA RADARSAlexander Praskovsky 1 and Eleanor Praskovskaya 21 National Center for Atmospheric Research, 3450 Mitchell Lane, Boulder, CO 80301, USA2 Colorado Research Associates, 3380 Mitchell Lane, Boulder, CO 80301, USARemote sensing of turbulence is a task of utmost importance for studying the atmosphere.The existing spaced antenna (SA) methods for atmospheric profiling radars produce directlyonly the intensity of the vertical turbulent velocity component while other characteristicssuch as the eddy dissipation rate, turbulent kinetic energy, and others are estimated using theisotropy, the dynamic equilibrium, and other assumptions; e.g., Hocking et al. (1989), Doviaket al. (1996), and references therein. In this paper we consider an application of the structurefunction(SF) based method UCAR-STARS (University Corporation for AtmosphericResearch - STructure function Analysis of Received Signals) to direct measurements of theintensity of three turbulent velocity components and the horizontal shear stress by SA radars.We present a development of the approach by Praskovsky and Praskovskaya (2003) belowreferred to as PP. To evaluate the proposed method, results for the NCAR Multiple AntennaProfiler (MAPR) in the atmospheric boundary layer (ABL) at a height of 300 m above theground are compared with simultaneous measurements by a sonic anemometer located atop a300-m tower 600 m distant from MAPR.302The transmitter of a SA profiling radar sends pulses of radio waves vertically upwards intothe atmosphere and these are scattered by the refractive index irregularities to form a movingand changing diffraction pattern on the ground. Following PP, the irregularities are referredto as scatterers independent of their physical nature. Each scatterer is characterized by itsrrinstantaneous location xi( t) = { xi( t), yi( t), zi( t)},velocity Wi() t = { Ui(), t Vi(), t Wi()},t andreflectivity ∆ ni( t). Hereafter t is time, i = 1, 2, ..., M, and M is the number of scatterers in theilluminated volume. The geophysical coordinate system with z axis directed upwards, x axistowards east, and y axis towards north is used hereafter; the values in the brackets {} denotethe Cartesian components of a vector. The magnitude and phase of the diffraction pattern issampled with N ≥ 3 spatially separated receiving antennas with the phase centers x rak ,wherek = 1, 2, ..., N denotes the receiver number. Each antenna provides a complex received signalrrI ( xak,, t) + −1 Q( xak,, t)where I and Q are the in-phase and quadrature components of thepure return from the scatterers with no noise or clutter. Equations for SF of pure signals canbe used directly in practical measurements while noise can be taken into account whilecalculating the SF (PP, sec. 4). Consider a pair of receivers with the phase centers x rak ,andx r am ,, k ≠ m = 1, 2, ..., N. The non-dimensional cross SF of order p ≥ 2 can be defined as:2p /2r r r r p r rDp( ∆ xmk, τ) = ⎡⎣Sx (a, k,) t− Sx (a, k+∆ xmk, t+ τ) ⎤⎦ ⎡Sx (a, k,) t−Sx (a,k,)t ⎤⎣ ⎦(1)r 2 r 2 rwhere Sx (ak ,, t) = I( xak ,, t) + Q( xak,, t)is the instantaneous power of pure received signals;∆ x r = x r −xr is a spatial separation between the antenna centers, τ is a temporalmk am , ak ,separation between the signals, and the brackets denote ensemble averages. The auto SFrDp, auto( xa,k, τ ) is a particular case of (1) at ∆xrmk= 0. SF for any atmospheric profiling radar atτ → 0 and small enough ∆xr mkcan be presented in the following form (PP, sec. 3):